Zoledronic acid, known as (1-hydroxy-2-imidazol-1-yl-1-phosphono-ethyl)phosphonic acid, is depicted by the following chemical structure:

Zoledronic acid is a third generation bisphosphonate which far exceeds the previous generations in terms of efficacy and is used predominately for indications of osteoporosis, Paget's disease, hypercalcemia, and inhibition of bone metastasis. It was originally developed by Novartis and marketed as the monohydrate under the brand names Zometa® and Reclast®. Zoledronic acid was first approved in 2000 for the treatment of hypercalcemia in Canada. It was later approved for use in the US for hypercalcemia in 2001, for multiple myeloma and bone metastases from solid tumors in 2002, and for osteoporosis and Paget's disease in 2007. Clinical trials have also been conducted or are on-going exploring the use of zoledronic acid in neoadjuvant or adjuvant cancer therapy, Coleman, et al., British J Cancer 2010; 102(7):1099-1105, Gnant, et al., New England J Medicine. 2009, 360 (17):679-691 and Davies, et al. J Clinical Oncology, 2010, 28(7s): Abstract 8021. Zoledronic acid is administered as an intravenous (IV) dose of 4 mg over 15 minutes per month for hypercalcemia of malignancy, multiple myeloma, and bone metastases from solid tumors, while an IV dose of 5 mg over 15 minutes is used for osteoporosis and Paget's disease.
Zoledronic acid is sparingly soluble in water and 0.1 N HCl solution but is freely soluble in 0.1 N NaOH. Zoledronic acid is practically insoluble in various organic solvents.
Much effort has been taken to generate novel oral formulations of zoledronic acid through crystallization and metal salt formation to improve its aqueous solubility, permeability, and subsequent oral bioavailability. A crystalline trihydrate was disclosed in the U.S. Patent application 2006/0178439 A1 and world patent application WO2007/032808. Seven hydrated forms, an amorphous form, three monosodium salts, and eleven disodium salts with varying degrees of hydration of zoledronic acid were also disclosed in the patent application WO2005/005447 A2. Zoledronate metal salts including Na+, Mg2+, Zn2+ were reported in the journal of Drugs of the Future (Sorbera et al, 25(3), Drugs of the Future, (2000)). Zoledronate, zoledronic, or zoledronic salt represents the ionic form of zoledronic acid. Patent application WO2008/064849 A1 from Novartis disclosed additional metal salts including two Ca′ salts, two Zn2+ salts, one Mg2+ salt, as well as a monohydrate, a trihydrate, an amorphous form, and an anhydrous form.
According to the US Food and Drug Administration (FDA) Summary Basis of Approval (SBA) for zoledronic acid, the poor oral bioavailability (approximately 1%), is partially due to its poor permeability in the GI tract. It was also noted that insoluble metal complexes were formed in the upper intestines, most commonly with calcium. Zoledronic acid has also been shown to cause severe gastric and intestinal irritations. In some cases the irritations were so severe that medical treatment was required.
Due to the fact that zoledronic acid is only available as a parenteral dosage form there is a clear need to develop novel forms of zoledronic acid that can be included in an oral dosage form particularly as the use of orally administered drugs are becoming more wide spread in many therapeutic areas including the treatment of cancer. The upward trend in the use of oral drugs will continue especially in light of the goal to decrease the overall cost of healthcare. Thus, there is an opportunity to create oral dosage forms of IV drugs where oral dosage forms do not yet exist due to their poor aqueous solubility and/or poor permeability providing a clear clinical benefit for patients.
Recent activity concerning the development of oral formulations has led to the use of medium chain fatty acids to enhance the drug's low permeability as disclosed in the US 2007/0134319 A1 and US 2007/0196464 patent applications. Additionally, Acylcarnitines have also been used for the same purpose as published in WO 00/61111 and P. Sinko et al; Pharmaceutical Research, Vol. 16, No. 4, 1999, P 527-533. Modified amino acid carriers, have also been employed to improve the absorption of the drug as shown in the WO 2007/093226 A1 application.
The development of oral forms of zoledronic acid has been problematic due to its poor aqueous solubility and permeability. By using pharmaceutically acceptable cocrystal formers to bond with pure zoledronic acid to create novel molecular complexes neutral and ionic (e.g. cocrystals, salts and solvates) which can improve solubility and/or permeability, the opportunity is therefore provided to tackle such problems and develop an oral dosage form.
All of the above attempts to improve the oral bioavailability of zoledronic acid were either focused on improving the aqueous solubility by generating novel solid forms, or by mixing the drug with an inactive ingredient that has enhanced GI tract permeability. The improvement of aqueous solubility failed to improve the bioavailability of zoledronic acid, since the formation of insoluble zoledronate calcium complexes is unlikely to be prevented. On the other hand, powder mixtures of the poorly permeable drug with inactive permeability enhancers improved the bioavailability of the drug. This approach of mixing different materials with different particle sizes and size distributions could result in poor blend/physical mixture uniformity. Constituents of the mixture could also segregate during transportation or with shaking and vibration. Additionally, the powder blends require that the ingredients are compatible and no potential for solid-solid interaction with or without atmospheric interferences exist thus impacting on their physical stability during storage or in a delivery system.
To the best of the inventors' knowledge, no attempt has been made prior to this invention towards a deliberate molecular design to create a molecular complex of the drug and additional component(s) (coformer(s)) in a single crystalline structure that is physically stable and is not influenced by the addition of excess coformer(s) in the formulation. The benefit of such design can lead to the elimination of all potential physical instability in the physical mix of the molecular complex and the coformer(s). Additionally, the resulting molecular complexes possess very different physicochemical properties compared to the parent drug, coformer or their physical mixture. These properties include but are not limited to melting point, thermal and electrical conductivity, aqueous solubility, rate of dissolution and permeability across the GI tract membrane.
Orally administered drugs are becoming more preferred in various therapeutic areas including cancers. Clearly, there is an opportunity to create oral dosage forms of IV drugs where oral dosage forms do not yet exist due to their poor aqueous solubility and/or poor permeability providing a clear clinical benefit for patients. Given the fact that zoledronic acid is only approved for IV administration, there is a need to develop an oral dosage form of zoledronic acid. By using pharmaceutically acceptable and/or approved coformers to hydrogen bond with zoledronic acid, novel molecular complexes (e.g. cocrystals, salts, solvates, and mixtures thereof) with improve solubility and/or permeability can be created. These novel molecular complexes could be used in the development of an oral dosage form for zoledronic acid.